We will characterize the clinical dose-response curves for the relief of parkinsonism and the production of dyskinesia as a function of levodopa 3-O-methyldopa levels in ten patients with advanced Parkinson's disease before and after undergoing stereotactic posteroventral pallidotomy. We will test the hypothesis that pallidotomy selectively shifts to the right the levodopa dose-response curve for dyskinesia without altering the dose response curve for the relief of parkinsonism. We have studied nine subjects so far. We anticipate studying 12 subjects in 1997. We have prepared one manuscript for publication, but it is currently being reviewed. There have been no unexpected adverse events.